Ink jet printers create an image on a surface by ejecting ink through orifices in a print head face plate, which communicates with a print head. To provide fine image resolution, the ejected ink droplets are very small, as are the orifices. Since the orifices are very small, an orifice can be partially or completely blocked by an air pocket or a small particle.
Solid ink printers melt solid ink and deliver the melted ink to the print head. The melted ink travels through channels and chambers in the print head towards the reservoirs. When the solid ink printer is turned off, the ink that remains in the print head can freeze. When the ink thaws in the print head, air that was once in solution in the ink can come out of solution to form air bubbles or air pockets in the print head.
An obstructed orifice can result in unacceptable printing. The obstruction, be it an air pocket or a small particle, can usually be removed by purging the orifices. In known print heads, a vacuum attaches to the face plate of the print head and the obstruction is removed by imparting a negative pressure on the face plate. The vacuum system is complicated requiring many different parts. Accordingly, it is desirable to purge the orifices, as well as other channels and chambers in the print head, by introducing a positive pressure into the ink channels of the print head to eject obstructions out of the orifices and the ink channels leading to the orifices.